Variations in tape drive speed affect the accuracy and fidelity of recording and reproduction of signals being transduced onto or from magnetic tape. Such external influences interfere with uniform passage, that is, with the uniformity of speed of magnetic tape in the guide path thereof. It has previously been proposed--see German Published patent application DE-AS No. 11 89 748--to utilize inertia masses which are of equal size and which operate at the same speed but in opposite direction of rotation, and which are coupled to the drive arrangement of the magnetic tape transport in order to eliminate undesirable variations in tape transport speed which, for simplicity, may be referred to as "flutter". The inertia masses should have as large a dimension and weight as possible; due to the dimensioning of the inertia masses and the speed with which they operate, it is difficult to fit the system into recording/reproducing apparatus, particularly if intended for portable use. Limitations arise with respect to the spatial arrangement of the inertia masses, coupling into the drive or operating chain which is coupled to drive the tape and/or the tape reels or spools thereof. It is particularly difficult to fit such inertia masses into a recorder if, in accordance with an example, the shaft of one of the inertia masses is also the shaft of an audio system, and the shaft of the counter-rotating mass is coupled to the drive of the take-up reel or its drive mechanism.
A flutter compensation system for magnetic tape apparatus in which the tape can operate in two directions of movement is described in German Patent Disclosure Document DE-OS No. 19 35 828 in which a common belt drives two inertia wheels in opposite direction of rotation. This arrangement is provided essentially for rapid change-over of the direction of tape movement; nothing is stated with respect to dimensioning the inertia masses or their speeds in order to suppress flutter or to compensate for external influences on the operating speed of the unit.
It has also been proposed to apply an inertia mass to the shaft controlling the speed of movement of an audio tape in an audio recording/reproducing apparatus--see German Patent Disclosure Document DE-OS No. 23 50 237--in which two inertia masses are coaxially positioned. The inertia masses operate in opposite directions of rotation. It is the intention to eliminate external effects which are due to torsion or tipping or tilting, as well as rotary changes of speed. Such an arrangement requires, however, a comparatively long drive belt or drive connection cable for the two inertia masses with several deflection or changeof-direction rollers. The highly desirable fixed and rigid coupling between the two inertia masses thus cannot be obtained. Further, the requirement for space to place the respective components as well as the weight are difficult to meet.
A tape recorder with an anti-flutter or speed variation mechanism is described in German Patent Disclosure Document DE-OS 29 30 896 in which the moment of inertia and angular speed of two oppositely rotating masses is determined and made equal. On the one hand, the rotary mass of the motor is used and, on the other, a separate flywheel concentric with the tape transport shaft. This arrangement is comparatively space-consuming and does not account for the influence of the rotating mass of the counter or engagement roller which is in contact with the tape and which, as is customary in such apparatus, presses the tape against the circumference of the drive capstan.